1. Field of the Invention
The invention relates to a transmitter arrangement for digitally modulated signals, and especially in a transmitter arrangement, whereby the modulation is a non-constant envelope modulation and the transmitter arrangement comprises a non-linear class C output amplifier and a control voltage generator.
2. Description of the Prior Art
In digital radio systems that do not use constant envelope modulation, the radio transmitter usually comprises linear class A or AB, in some instances linearized class C amplifiers. Such modulation schemes include e.g. schemes of the QAM-type (Quadrature Amplitude Modulation), where the modulated information exists both in the signal phase and in the signal amplitude. A modulation scheme of this kind has been proposed to be used in the future North-American digital mobile radiotelephone system.
Linear amplifiers have a poor efficiency compared to a non-linear amplifier operating in class C. On the other hand, linearized class C amplifiers generally lead to complicated designs.